Question 13103 of 790 · California General Electrician Exam
A 45 kVA, three-phase, 480 volt primary transformer (1,000 volts or less) is protected on the primary side only. What is the maximum primary overcurrent device, using the next-higher-standard-size note?
Exactly one answer is correct.
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Correct answer to question 13103
- C: 70 A
Explanation
Primary current is 45,000 / (480 x 1.732) = 54.1 A, and primary-only protection is limited to 125 %: 54.1 x 1.25 = 67.7 A. Because that is not a standard size, the next higher standard rating of 70 A is allowed.
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